French link snaffle!
I've ridden my boy in an eggbutt and D-Ring single-link snaffle bits, but I still don't feel like he likes them. After I got him and was working him more than he'd been worked in the past, he started foaming up a LOT - I wasn't using a copper bit, and we came to the conclusion it was because of stress. Since then, I've been riding bitless, first with a hackamore, but mostly with a sidepull. Though I plan on continuing with the sidepull, I'd really like to have a bit he's comfortable in.
I didn't use a bit on him all summer and fall and only just started using one again for training. He's not foaming up, but I'm keeping an eye out for that. However, he is pulling his lips back after I put the bridle on and often when I'm riding, whether or not I'm making any contact with the reins. He also chews on the bit a lot. The pictures below aren't of my horse, but are good examples of how he used to foam up last Spring before I switching him to being bitless and how he still continues to pull his lips back.
I'm thinking of getting a French Link Snaffle, maybe even copper, but have never had bit issues before so don't have a lot of experience solving them.